Fluid compositions containing a cyclopolysiloxane



nited States atent ice FLUID COMPOSITIONS CONTAINING A CYCLOPOLYSILOXANE Robert L. Merker, Bellevue, Pa., and William A. Zisman, Washington, D. C.

No Drawing. Application June 18, 1953, Serial No. 362,697

9 Claims. (Cl. 252-40.7)

This invention relates to new fluid compositions having lubricating properties, more particularly to improved aliphatic ester oils and greases.

The aliphatic ester oils to which reference is made herein and with which the present invention is concerned are liquid saturated aliphatic normal esters of saturated aliphatic carboxylic acids which esters are fur ther defined by the fact that their boiling point is 150 C. or higher. This class of liquid aliphatic esters has been recognized by the art as a source of synthetic lubricating oils and some of these esters have been used with metal soaps for making greases. The art is also aware that metal soaps accelerate the thermal oxidation of these liquid aliphatic esters and has added antioxidants to the greases to improve their oxidation stability.

The present invention has as an object the provision of a new class of antioxidants for improving the oxidation stability of the aliphatic ester oils which contain metal soaps, especially at elevated temperatures. A further object is the provision of aliphatic ester oil greases which have enhanced oxidation stability at elevated temperatures. Other objects will appear hereinafter from the description of the invention.

We have found that the oxidation stability at elevated temperatures of aliphatic ester oils containing metal soaps can be improved by the addition thereto of small amounts of an aromatic cyclopolysiloxane which contains aromatic groups on at least half of the silicon atoms and lower alkyl groups or any not so substituted. The new antioxidants may be trimers, tetramers, pentamers, etc., in which the aromatic groups may be, for example, phenyl, naphthyl, diphenyl, tolyl, xylyl, cyclohexylphenyl, anisyl, phenoxyphenyl, hydroxyphenyl, carboxyphenyl, carbethoxyphenyl, nitrophenyl, aminophenyl, N-methylaminophenyl, N-phenylaminophenyl, etc. A preferred group of the aromatic cyclopolysiloxanes are those in which the aromatic groups are aryl or lower alkaryl, more preferably, phenyl and lower alkylphenly, for example, methyl, ethyl, propyl, butyl, tertiary butyl and hexylphenyl groups. Where lower alkyl groups are present on silicon atoms of the cyclopolysiloxanes they may contain up to 6 carbon atoms, for example, methyl, ethyl, propyl, tertiary butyl, hexyl, etc. Within this preferred group of aromatic cyclopolysiloxanes is to be mentioned in particular, hexaphenyl cyclotrisiloxane.

The stability to oxidation, especially at elevated temperatures, e. g. at 80 to 150 C., of the aliphatic ester oil-metal soap compositions can be enhanced by the addition thereto of one of the antioxidant cyclopolysiloxanes in concentrations within the range of about 0.1 and 10% by weight therein, with a preferred general range for the addition of the antioxidant being from about 0.1 to 5% by weight. The amount of the antioxidant added will depend upon the activity of the individual cyclopolysiloxanes and the particular aliphatic ester oil-metal soap composition. Depending upon the particular cyclopolysiloxane compound,'the antioxidant is dissolved to a greater or lesser extent in the aliphatic ester oil or dispersed therein.

The aliphatic ester oils of the compositions of the invention may be prepared by complete esterification in known way between the corresponding saturated aliphatic carboxylic acids, for example, butyric, oxalic, adipic, 3- methyladipic, azelaic, tricarballylic acids, etc., and the corresponding saturated aliphatic alcohols, for example, methanol, Z-ethylhexanol, ethyleneglycol, glycerol, pentaethrythritol, etc.; the acids and the alcohols being selected so as to obtain the desired liquid normal ester as will be understood by those skilled in the art. A class of esters of particular interest for the compositions of the present invention are the liquid saturated aliphatic diesters of the saturated aliphatic dicarboxylic acids which have an alkylene chain of 3 or more carbon atoms, more especially those which are straight or branched chain alkyl diesters of the 5 to 12 carbon atom alkylene dicarboxylic acids in which the alkylene chain may be branched or unbranched and which have the general formula:

wherein R4. is a bivalent aliphatic hydrocarbon radical or" 3 to 10 carbon atoms chain length. Illustrative of this latter group of dibasic acids are, for example, 2- methylglutaric, adipic, S-methyladipic, pimelic, Z-ethylglutaric, suberic, azelaic and sebacic acids, etc. Illustrative of the liquid aliphatic esters with which the invention is concerned are, for example, ethyl myristate, octadecyl acetate, diethyl oxalate, dipropyl malonate, dibutyl-3-methyl gultarate, diethyl adipate, di-Z-ethylhexyl adipate, diethyl pimelate, di-Z-ethylhexyl azelate, di-Z- ethylhexyl sebacate, di-(3,5,5-trirnethylhexyl) sebacate, 2,4-pentanediol dihexanoate, triamyl tricarbllylate, pentaethryritol tetrahexanoiate, etc.

The metal soap in the compositions of the invention may be any of the metal salts of the soap-forming fatty and hydroxy fatty acids, for example, the calcium, strontium, barium, sodium, potassium, lithium, copper, tin, lead, zinc, aluminum, etc., salts of lauric, myristic, palmitic, oleic, ricinoleic, stearic, arachidic, behenic, erucic, l2-hydroxy stearic acid, etc., or of mixtures of these acids. The amount of the metal soap in the com positions may be widely varied and range from as little as about 0.1% by weight up to a practical maximum. In the case of lubricating greases, the metal soap content of the compositions will generally be from about 5 to 30% by weight, for which usually there is employed one of the alkaline earth or alkali metal soaps, for example,

calcium, strontium, barium, sodium and lithium stearates. I

The invention is illustrated in greater detail by the following specific example in which an aromatic cyclopolysiloxane was incorporated in a lithium soap-diester grease and subjected to an accelerated oxidation test to deter-' mine its efficacy as an antioxidant for the'metal soapdiester oil composition at elevated temperatures. The greases were prepared in conventional manner by heating the aliphatic ester oil and metal soap together under stirring to form a clear solution, quickly cooling the solution to form a gel and working the gel through a screen to obtain a grease of uniform consistency (about 10 workings through a Hain Microworker). The antioxidant was mixed into the grease and the whole then worked through the screen as before to obtain uniformity of admixture. The control grease or blank was made up to contain the same relative proportion of the metal soap and diester oil but without the presence of the cyclopolysiloxane antioxidant. The accelerated oxidation test was carried out in accordance with Navy Specification AN-G-3a(2) using a Norma-Hoffman bomb apparatus.

, ane.

Example A grease was prepared to contain 16.2 mol per cent (11.12% by weight) lithium stearate, 80.8 mol percent (87.68% by weight) di-2-ethylhexyl sebacate and 3.0 mol per cent (1.2% by weight) hexaphenyl cyclotrisilox- A control grease was made up in the same manner to contain only lithium stearate and di-2-ethylhexyl sebacate in the same relative proportions.

Twenty gram samples of each of the two greases were placed in separate Norma-Hoffman bombs which were then sealed, heated to 100 C. and oxygen pressed thereinto at 110 bombs per square inch. The oxidation test was run for a period of 300 hours during which time the temperature in the bombs was maintained at 100 C.i0.5 C.

Bomb. pressure readings were made at intervals over the 300 hour period, which readings were accurate to :10 p. s. i. Consumption of oxygen by the grease and thereby oxidation of the same is indicated by drop in the oxygen pressure in the bomb. Readings of the pressure in the bomb containing the control grease showed a rather sharp drop even in the earlier stages of the run (up to 50 hours) which was progressive until at the end of the 300 hours the pressure had dropped to 50 pounds per square inch, indicating a substantial amount of oxidation to have taken place in the unprotected grease. On the other hand, pressure readings in the bomb contain ing the grease to which the hexaphenyl cyclotrisiloxane had been added showed a drop in pressure of 18 pounds p. s. i. over the 300 hour period, indicating the cyclopolysiloxane compound to be an eifective antioxidant for the grease.

The aliphatic ester oil-metal soap compositions of the present invention may be blended with miscible proportions of other lubricating oils, such as petroleum oils and polyoxyalkylene oxides having one or both terminals ending in an alkyl ether group, e. g., the butoxy group. Antioxidants of types other than the aromatic cyclopolysiloxanes may be used in the compositions in conjunction with the latter, such as phenolic and aromatic amine type antioxidants which are active as antioxidants at the lower temperatures, e. g., below 100 C., and thereby will impart supplemental protection to the aliphatic ester oilmetal soap compositions at temperatures occurring during storage or during other low temperature non-operating periods, e. g., cyclohexylphenol, p-hydroxy diphenyl, 4-t-butyl-2-phenylphenol, thymol, catechol, phenly-anapthylamine, etc. Other antioxidant compounds of the non-silicon type are dialkyl selenides, e. g., dilauryl selenide, and phenothiazine. Some of these supplemental antioxidant compounds are active at the elevated temperatures also, for example, dilauryl selenide and phenothiazine.

While in the foregoing description we have made reference to certain specific embodiments of the invention, these are intended by way of illustration and not in limitation since the invention may be variously embodied without departing from the spirit or scope of the appended claims.

The invention described herein may be manufactured and used by or for the Government of the United States 4. of America for governmental purposes without the payment of any royalties thereon or therefor.

What we claim is:

1. A fluid composition comprising a liquid saturated aliphatic normal ester of a saturated aliphatic carboxylic acid, which ester has a boiling point not lower than 150 C., at least about 0.1% by weight of a metal soap and a small amount, suflicient to improve the oxidation stability of the ester-soap composition at elevated temperatures, of an aromatic cyclopolysiloxane in which at least half of the silicon atoms are attached to aromatic groups and any remainder to lower alkyl groups of up to 6 carbon atoms.

2. A fluid composition as defined in claim 1, wherein the liquid ester is an alkyl diester of a saturated aliphatic dicarboxylic acid.

3. A fluid composition as defined in claim 1, wherein the liquid ester is a branched chain alkyl diester of a saturated aliphatic dicarboxylic acid.

4. A fluid composition comprising a liquid branched chain alkyl diester of a saturated aliphatic dicarboxylic acid, which ester has a boiling point not lower than 150 C., at least about 0.1% by weight of a metal soap and a small amount, sufficient to improve the oxidation stability of the ester-soap composition at elevated temperatures, of a cyclopolysiloxane in which at least half of the silicon atoms are attached to aryl groups and any remainder to lower alkyl groups of up to 6 carbon atoms.

5. A fluid composition as defined in claim 4, wherein the aryl groups on the silicon atoms of the cyclopolysiloxane are phenyl groups.

6. A fluid composition comprising a liquid branched chain alkyl diester of a saturated aliphatic dicarboxylic acid, which ester has a boiling point not lower than 150 C., at least about 0.1% by weight of a metal soap and a small amount, sufficient to improve the oxidation stability of the ester-soap composition at elevated temperatures, of hexaphenyl cyclotrisiloxane.

7. A grease composition comprising a liquid branched chain alkyl diester of a dicarboxylic acid of the formula:

wherein R4 is a bivalent aliphatic hydrocarbon radical of from 3 to 10 carbon atoms chain length, which ester has a boilingpoint not lower than 150 C. and is thickened with a metal soap selected from the group consisting of alkaline earth and alkali metal soaps, and a small amount, sufiicient to improve the oxidation stability of the ester-soap composition at elevated temperatures, of a cyclopolysiloxane in which at least half of the silicon atoms are attached to phenyl groups and any remainder to lower alkyl groups of up to 6 carbon atoms.

8. A grease composition as defined in claim 7, wherein the cyclopolysiloxane is hexaphenyl cyclotrisiloxane.

9. A grease composition as defined in claim 7, wherein the cyclopolysiloxane is octaphenyl cyclotetrasiloxane.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A FLUID COMPOSITION COMPRISING A LIQUID SATURATED ALIPHATIC NORMAL ESTER OF A SATURATED ALIPHATIC CARBOXYLIC ACID, WHICH ESTER HAS A BOILING POINT NOT LOWER THAN 150* C., AT LEAST ABOUT 0.1% BY WEIGHT OF A METAL SOAP AND A SMALL AMOUNT, SUFFICIENT TO IMPROVE THE OXIDATION STABILITY OF THE ESTER-SOAP COMPOSITION AT ELEVATED TEMPERATURES, OF AN AROMATIC CYCLOPOLYSILOXANE IN WHICH AT LEAST HALF OF THE SILICON ATOMS ARE ATTACHED TO AROMATIC GROUPS AND ANY REMAINDER TO LOWER ALKYL GROUPS OF UP TO 6 CARBON ATOMS. 